Method for forming color cholesteric liquid crystal display devices

ABSTRACT

The invention provide a fabrication method for a color cholesteric liquid crystal display device, comprising: providing a first substrate; forming a patterned enclosed structure on the first substrate, wherein the patterned enclosed structure comprises a plurality of stripe wall structures, and one end of each stripe wall structure is connected to and perpendicular to a straight seal line, thereby dividing a first LC channel with a first opening, a second closed LC channel, and a third closed LC channel, and the length of the first LC channel exceeds that of the second LC channel, and the length of the second LC channel exceeds that of the third LC channel; providing a second substrate with an adhesion layer formed thereon; assembling the first substrate and the second substrate to tightly seal the adhesion layer and the patterned enclosed structure.

This application is a Divisional application of pending U.S. patentapplication Ser. No. 11/950,270, filed Dec. 4, 2007 and entitled “COLORCHOLESTERIC LIQUID CRYSTAL DISPLAY DEVICES AND FABRICATION METHODSTHEREOF”.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to liquid crystal display (LCD) devices, and inparticular to single layer color cholesteric liquid crystal displaydevices and fabrication methods thereof.

2. Description of the Related Art

Liquid crystal display (LCD) devices have many advantages such as asmaller size, lighter weight and lower power consumption, and areapplicable in a variety of electronic and communication devicesincluding notebook computers, personal digital assistants (PDA), mobilephones and the like due to its lighter weight, thinner profile, andportability. Conventional reflective memorable color liquid crystaldisplay devices are widely applicable in electronic books, electronicpapers, and the likes. The structures and fabrication methods ofconventional cholesteric liquid crystal display devices use atri-layered red (R), green (G), and blue (B) pixel stacked structurecorresponding to various different driving methods. However, stackingtri-layered R, G, and B pixels may result in optical aberration andmisalignment during fabrication. Moreover, the tri-layered R, G, and Bliquid crystal layer stacked structure are so complicated that layout ofelectrodes is difficult to design and an LCD panel using the stackedstructure has a rigid port, resulting in an intricate fabricationprocesses and high fabrication costs.

Accordingly, the use of single layer color cholesteric liquid crystaldisplay devices and fabrication methods thereof can effectivelyameliorate optical aberration, simplify the fabrication process, andreduce fabrication costs. Particularly, the device is applicable to thefield of color flexible LCD devices. U.S. Pat. No. 5,825,451, theentirety of which is hereby incorporated by reference, discloses asingle layer color cholesteric LCD device using a combination of lightdecomposable/polymerizable chiral agents and single layer cholesteric LCstructure. The single layer color cholesteric LCD device is illuminatedby a UV light disrupting or reducing contents of chiral agent at asingle region to achieve colorizing of single layer cholesteric LCDdevice. However, the single layer color cholesteric LCD device is easilyaffected by ambient light deteriorating display stability thereof.

U.S. Pat. No. 6,741,321, the entirety of which is hereby incorporated byreference, discloses an LCD device using a single LC layer and a doublesubstrate assembly process. Different color LC materials arerespectively injected into LC channels during fabrication. However, thesingle layer LCD assembly is not sealed enough such that overflow occursbetween adjacent LC channels resulting in color mixing and reduced colorsaturation.

FIG. 1A is a cross section of a conventional single layer colorcholesteric LCD device. Referring to FIG. 1A, a conventional singlelayer color cholesteric LCD panel 2 includes a lower substrate 6 and anupper substrate 12 opposed to each other and with a gap therebetween. Anenclosed structure 8 is interposed between the lower substrate 6 and theupper substrate 12, dividing a plurality of stripe color sub-pixel LCchannels. A first electrode 4 and an alignment layer 14 are disposed onthe lower substrate 6. A second electrode 10 and an alignment layer 14are disposed on the upper substrate 6. The first electrode 4 and thesecond electrode 10 are substantially perpendicular to each other.

FIG. 1B is a schematic view of the lower substrate of the conventionalsingle layer color cholesteric LCD device of FIG. 1A. In FIG. 1B, theenclosed structure 8 divides a plurality of (R, G, B) stripe colorsub-pixel LC channels C_(R), C_(G), and C_(B). Perpendicularly crossedsegments 16 and 18 are disposed on one end of the LC channels C_(G) andC_(B) to seal the LC channels. After the lower substrate 6 and uppersubstrate 12 are assembled, the second end L₂ of the enclosed structure8 are sealed by a sealant enclosing the LC channels C_(G) and C_(B),while the first end L₁ of the LC channels C_(R) remains opened to serveas an LC injection opening. Each of the LC channels C_(R), C_(G), andC_(B) is sequentially injected with respective color LC and sealed.Before filling each of the single layer color LC channels, however,conventional methods require sealing of the second end of the enclosedstructure. Furthermore, when separately injection LC into the LCchannels, different color LCs may overflow to adjacent LC channels andmix, thus resulting in color mixing and reduced color saturation.

BRIEF SUMMARY OF THE INVENTION

A detailed description is given in the following embodiments withreference to the accompanying drawings.

The features and aspects of the invention are related to single layercolor cholesteric liquid crystal display devices and fabrication methodsthereof. Different length liquid crystal (LC) channels are formed bypatterning enclosed structure on a substrate, and an adhesion layer isformed on another opposing substrate. The two opposing substrate areassembled. The assembled structure is sequentially cut, injected red,green, and blue LC, and sealed to prevent color mixing and reduce colorsaturation.

Embodiments of the invention provide a color cholesteric liquid crystaldisplay device, comprising: a first substrate, a second substrateopposed to each other with a gap therebetween; a patterned enclosedstructure interposed between the first substrate and the secondsubstrate dividing a plurality of color sub-pixel channels; and aplurality of color cholesteric liquid crystals respectively filled ineach of the color sub-pixel channel; wherein an adhesion layer istightly adhered between the second substrate and the patterned enclosedstructure so as to prevent mixing of the color cholesteric liquidcrystals between adjacent color sub-pixel channels.

Embodiments of the invention also provide a fabrication method for acolor cholesteric liquid crystal display device, comprising: providing afirst substrate; forming a patterned enclosed structure on the firstsubstrate, wherein the patterned enclosed structure comprises aplurality of stripe wall structures, and one end of each stripe wallstructure is connected to and perpendicular to a straight seal line,thereby dividing a first LC channel with a first opening, a secondclosed LC channel, and a third closed LC channel, and the length of thefirst LC channel exceeds that of the second LC channel, and the lengthof the second LC channel exceeds that of the third LC channel; providinga second substrate with an adhesion layer formed thereon; assembling thefirst substrate and the second substrate to tightly seal the adhesionlayer and the patterned enclosed structure; injecting a first colorliquid crystal in the first LC channel and sealing the first LC channelwith a first seal material; cutting the assembly to expose a secondopening of the second LC channel; injecting a second color liquidcrystal in the second LC channel and sealing the second LC channel witha second seal material; cutting the assembly to expose a third openingof the third LC channel; and injecting a third color liquid crystal inthe third LC channel and sealing the third LC channel with a third sealmaterial.

Embodiments of the invention further provide a fabrication method for acolor cholesteric liquid crystal display device, comprising: providing afirst substrate; forming a patterned enclosed structure on the firstsubstrate, wherein the patterned enclosed structure comprises aplurality of stripe wall structures, and one end of each stripe wallstructure is connected to and perpendicular to a straight seal line,thereby dividing a first LC channel with a first opening, a secondclosed LC channel, and a third LC channel, and the length of the firstLC channel exceeds that of the second LC channel, and the length of thesecond LC channel exceeds that of the third LC channel; providing asecond substrate with an adhesion layer formed thereon; assembling thefirst substrate and the second substrate to tightly seal the adhesionand the patterned enclosed structure; injecting a first color liquidcrystal in the first LC channel; polymerizing the first color liquidcrystal; cutting the assembly to expose a second opening of the secondLC channel; injecting a second color liquid crystal in the second LCchannel; polymerizing the second color liquid crystal; cutting theassembly to expose a third opening of the third LC channel; injecting athird color liquid crystal in the third closed LC channel; andpolymerizing the third color liquid crystal.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be more fully understood by reading the subsequentdetailed description and examples with references made to theaccompanying drawings, wherein:

FIG. 1A is a cross section of a conventional single layer colorcholesteric LCD device;

FIG. 1B is a schematic view of the lower substrate of the conventionalsingle layer color cholesteric LCD device of FIG. 1A;

FIG. 2 is a flowchart illustrating an exemplary embodiment of afabrication method for a single layer color cholesteric LCD deviceaccording to the invention;

FIGS. 3A-3D are schematic views of an exemplary embodiment of eachassembly step of the first and second substrate structures of theinvention;

FIG. 4 is a plan view of an embodiment of the enclosed structure of theinvention;

FIG. 5 is a cross section of an embodiment of the substrate structureassembly taken along A-A line of FIG. 4;

FIGS. 6A-6C are schematic views of an embodiment of each step ofinjecting each color LC into respective LC channels of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The following description is of the best-contemplated mode of carryingout the invention. This description is made for the purpose ofillustrating the general principles of the invention and should not betaken in a limiting sense. The scope of the invention is best determinedby reference to the appended claims.

FIG. 2 is a flowchart illustrating an exemplary embodiment of afabrication method for a single layer color cholesteric LCD deviceaccording to the invention. First, preparation of a first substratestructure (such as an upper substrate structure) is proceeded includingproviding a first substrate (S210) and forming a patterned firstelectrode along the first direction on the first substrate (S212).Subsequently, a first alignment layer is formed on the first substratecovering the first electrode (S214). A patterned enclosed structure or abank structure is then formed on the first substrate (S216). Thepatterned enclosed structure includes a plurality of stripe wallstructures, and one end of each stripe wall structure is connected toand perpendicular to a straight seal line, thereby dividing a first LCchannel with a first opening, a second closed LC channel, and a thirdclosed LC channel.

Subsequently, preparation of a second substrate structure (such as alower substrate structure) is proceeded including providing a firstsubstrate (S220) and forming a patterned second electrode along thesecond direction on the second substrate (S222). A second alignmentlayer is formed on the second substrate covering the second electrode(S224), and an adhesion layer is formed overlying the second substrate(S226).

The first and second substrate structures are assembled opposed to eachother with a gap interposed therebetween (S230). The patterned enclosedstructure and the adhesion layer are tightly combined to preventinjection of color LCs in adjacent LC channels from overflowing. A firstcolor cholesteric LC is filled in a first stripe LC channel and thensealed (S240). The assembly structure is cut to expose a second stripeLC channel (S250). A second color cholesteric LC is filled in the secondstripe LC channel and then sealed (S260). The assembly structure is cutto expose a third stripe LC channel (S270). A third color cholesteric LCis filled in the third stripe LC channel and then sealed (S280). Afterall the three color cholesteric LCs are filled and sealed, fabricationof the single layer color cholesteric LCD device is completed.

FIGS. 3A-3D are schematic views of an exemplary embodiment of eachassembly step of the first and second substrate structures of theinvention. Referring to FIG. 3A, a patterned enclosed structure 320 or abank structure is formed on the first substrate. The patterned enclosedstructure 320 comprises a plurality of stripe wall structures 324. Oneend of each stripe wall structures 324 connects to and is perpendicularto a straight end line 322 to divide a first LC channel C₁ with a firstLC injection opening, a second closed LC channel C₂, and a third closedLC channel C₃. The length of the first LC channel C₁ exceeds that of thesecond LC channel C₂, and the length of the second LC channel C₂ exceedsthat of the third LC channel C₃. The first substrate can be made ofrigid substrates or flexible soft substrates. For example, the flexiblesoft substrates comprise polycarbonate (PC) substrates, polyethersulfone(PES) substrates, polyethylene terephthalate (PET) substrates, andpolyimide (PI) substrates.

The first substrate may further comprise circuit elements forcontrolling pixel electrodes such as a thin film transistor (TFT) and acapacitor. Alternatively and optionally, the first substrate comprisespixel electrodes such as linear first electrodes along a first directionand a first alignment layer overlying the first substrate. The patternedenclosed structure can be formed by any well-known patterning processessuch as lithography and screen printing, and can be made of aphotoresist material.

Referring to FIG. 3B, a second substrate 350 including a rigid substrateor a flexible soft substrate is provided. The second substrate 350 cancomprises common electrodes, such as linear second electrodes along asecond direction and a second alignment layer overlying the secondsubstrate. The first direction and the second direction aresubstantially perpendicular to each other. Subsequently, an adhesionlayer 360 is formed on the second substrate 350 as shown in FIG. 3C. Theadhesion layer 360 is made of a glue material or a solidified material.For example, the solidified material comprises a light solidifiedmaterial or a thermoset material. The thickness of the adhesion layer350 is less than the thickness (height) of the patterned enclosedstructure 320.

Referring to FIG. 3D, the first substrate 310 and second substrate 320are assembled opposing each other such that the patterned enclosedstructure 320 and the adhesion layer 360 are tightly combined to preventLC overflow between adjacent LC channels during injection of color LCs.

FIG. 4 is a plan view of an embodiment of the enclosed structure of theinvention. In FIG. 4, a patterned enclosed structure 420 comprises aplurality of stripe wall structures 410. One end of each stripe wallstructures 410 connects to and is perpendicular to a straight end line422 and the other end of the stripe wall structures 410 connects to abulk region 440, thereby dividing a first LC channel C₁ with a first LCinjection opening, a second closed LC channel C₂, and a third closed LCchannel C₃. The length of the first LC channel C₁ exceeds that of thesecond LC channel C₂, and the length of the second LC channel C₂ exceedsthat of the third LC channel C₃. The bulk region 440 can enhanceadhesion between the patterned enclosed structure and the adhesivelayer, thereby preventing LC overflow between adjacent LC channelsduring injection of color LCs.

FIG. 5 is a cross section of an embodiment of the substrate structureassembly taken along A-A line of FIG. 4. Referring to FIG. 5, thecombination of the first and second substrate structure includes thefirst substrate 510 and second substrate 550 opposed to each other witha plurality of parallel LC channel 540 for containing respective colorLCs interposed therebetween. A linear electrode 520 such as a pixelelectrode along the first direction is disposed on the first substrate510. A linear electrode 560 such as a common electrode along the seconddirection is disposed on the second substrate 550. The patternedenclosed structure 530 and the adhesion layer 570 between the firstsubstrate 510 and second substrate 550 are tightly combined to preventLC overflow between adjacent LC channels during injection of color LCs.

FIGS. 6A-6C are schematic views of an embodiment of each step ofinjecting each color LC into respective LC channels of the invention.Referring to FIG. 6A, a first color (e.g., red) cholestic LC 490R isejected into a first LC channel, and the first LC channel is then sealedby a first sealant 480 a. For example, a red cholesteric CL materialcomprises mixture of red dye and twisted nematic liquid crystal layerdoped with chiral agent. The first sealant 480 a can comprise a lightsolidified material or a thermoset material. Next, a first cuttingprocedure is performed such as along cutting line B-B to uncover thesecond stripe LC channel C₂. The first cutting procedure can beperformed by dice-cutting and laser-cutting.

Referring to FIG. 6B, a second color (e.g., green) cholestic LC 490G isejected into a second LC channel, and the second LC channel is thensealed by a second sealant 480 b. For example, a green cholesteric CLmaterial comprises mixture of green dye and twisted nematic liquidcrystal layer doped with chiral agent. The second sealant 480 b cancomprise a light solidified material or a thermoset material. Next, asecond cutting procedure is performed such as along cutting line C-C touncover the third stripe LC channel C₃. The second cutting procedure canbe performed by dice-cutting and laser-cutting.

Referring to FIG. 6C, a third color (e.g., blue) cholestic LC 490B isejected into a third LC channel, and the third LC channel is then sealedby a third sealant 480 c. For example, a blue cholesteric CL materialcomprises mixture of blue dye and twisted nematic liquid crystal layerdoped with chiral agent. The third sealant 480 c can comprise a lightsolidified material or a thermoset material. After all the three colorcholesteric LCs are filled and sealed, fabrication of the single layercolor cholesteric LCD device is completed.

Note that in the abovementioned description in some embodiments, eachcolor cholesteric LC layer of the invention can further comprise polymerdispersed liquid crystal (PDLC) material. An LC fluid containing monomeror oligomer units would be injected into stripe LC channels. Afterilluminated by UV light, the LC fluid containing monomer or oligomerunits is polymerized into polymer dispersed liquid crystal (PDLC). UsingPDLC can omit sealing procedures of each stripe LC channel. For example,after the first and second substrate structures are assembled, a firstcolor liquid crystal is injected into the first LC channel. After thefirst color liquid crystal is polymerized, the assembly is cut touncover a second opening of the second LC channel. Next, a second colorliquid crystal is injected into the second LC channel. After the secondcolor liquid crystal is polymerized, the assembly is cut to uncover athird opening of the third LC channel. A third color liquid crystal isinjected into the third closed LC channel. The third color liquidcrystal is then polymerized. After all the three color cholesteric LCare filled and sealed, fabrication of the single layer color cholestericLCD device is completed.

Note that there are additional steps not mentioned here, which arerequired to complete the single layer color cholesteric LCD device, butwhich are not essential to an understanding of the invention and arewell-known to those with ordinary skill in the art.

Embodiments of the invention are advantageous in that an enclosedstructure dividing different length of LC injection channels is formedon one substrate, and an adhesion layer is applied on the othersubstrate. After the two opposing substrate are assembled, the enclosedstructure and the adhesion layer are tightly combined to prevent LCoverflow between adjacent LC channels during injection of color LCs. Theassembled structure is sequentially cut, injected red, green, and blueLC, and sealed to prevent color mixing and reduce color saturation.Thus, simplifying fabrication processes and reducing production costs.

While the invention has been described by way of example and in terms ofthe several embodiments, it is to be understood that the invention isnot limited to the disclosed embodiments. To the contrary, it isintended to cover various modifications and similar arrangements (aswould be apparent to those skilled in the art). Therefore, the scope ofthe appended claims should be accorded the broadest interpretation so asto encompass all such modifications and similar arrangements.

1. A fabrication method for a color cholesteric liquid crystal displaydevice, comprising: providing a first substrate; forming a patternedenclosed structure on the first substrate, wherein the patternedenclosed structure comprises a plurality of stripe wall structures, andone end of each stripe wall structure is connected to and perpendicularto a straight seal line, thereby dividing a first LC channel with afirst opening, a second closed LC channel, and a third closed LCchannel, and the length of the first LC channel exceeds that of thesecond LC channel, and the length of the second LC channel exceeds thatof the third LC channel; providing a second substrate with an adhesionlayer formed thereon; assembling the first substrate and the secondsubstrate to tightly seal the adhesion layer and the patterned enclosedstructure; injecting a first color liquid crystal in the first LCchannel and sealing the first LC channel with a first seal material;cutting the assembly to expose a second opening of the second LCchannel; injecting a second color liquid crystal in the second LCchannel and sealing the second LC channel with a second seal material;cutting the assembly to expose a third opening of the third LC channel;and injecting a third color liquid crystal in the third LC channel andsealing the third LC channel with a third seal material.
 2. Thefabrication method for a color cholesteric liquid crystal display deviceas claimed in claim 1, wherein the first substrate and the secondsubstrate are made of rigid substrates or flexible substrates.
 3. Thefabrication method for a color cholesteric liquid crystal display deviceas claimed in claim 2, wherein the flexible substrates comprise apolycarbonate (PC) substrate, a polyethersulfone (PES) substrate, apolyethylene terephthalate (PET) substrate, and a polyimide (PI)substrate.
 4. The fabrication method for a color cholesteric liquidcrystal display device as claimed in claim 1, wherein the adhesion layeris made of a glue material or a solidified material.
 5. The fabricationmethod for a color cholesteric liquid crystal display device as claimedin claim 4, wherein the solidified material comprises a light solidifiedmaterial or a thermoset material.
 6. The fabrication method for a colorcholesteric liquid crystal display device as claimed in claim 1, whereinthe thickness of the adhesion layer is less than the thickness of thepatterned enclosed structure.
 7. The fabrication method for a colorcholesteric liquid crystal display device as claimed in claim 1, whereinthe patterned enclosed structure comprises photoresist materials.
 8. Thefabrication method for a color cholesteric liquid crystal display deviceas claimed in claim 1, wherein the first color liquid crystal comprisesa red liquid crystal, the second color liquid crystal comprises a greenliquid crystal, and the third color liquid crystal comprises a blueliquid crystal.
 9. The fabrication method for a color cholesteric liquidcrystal display device as claimed in claim 8, wherein each of the redliquid crystal, the green liquid crystal, and the a blue liquid crystalcomprises a respective color dye and a twisted nematic liquid crystallayer doped with a chiral agent.
 10. The fabrication method for a colorcholesteric liquid crystal display device as claimed in claim 1, whereinthe first seal material, the second seal material, and the third sealmaterial comprises a light solidified material or a thermoset material.11. The fabrication method for a color cholesteric liquid crystaldisplay device as claimed in claim 1, wherein the step of cutting theassembly comprises dice-cutting and laser-cutting.
 12. A fabricationmethod for a color cholesteric liquid crystal display device,comprising: providing a first substrate; forming a patterned enclosedstructure on the first substrate, wherein the patterned enclosedstructure comprises a plurality of stripe wall structures, and one endof each stripe wall structure is connected to and perpendicular to astraight seal line, thereby dividing a first LC channel with a firstopening, a second closed LC channel, and a third closed LC channel, andthe length of the first LC channel exceeds that of the second LCchannel, and the length of the second LC channel exceeds that of thethird LC channel; providing a second substrate with an adhesion layerformed thereon; assembling the first substrate and the second substrateto tightly seal the adhesion and the patterned enclosed structure;injecting a first color liquid crystal in the first LC channel;polymerizing the first color liquid crystal; cutting the assembly toexpose a second opening of the second LC channel; injecting a secondcolor liquid crystal in the second LC channel; polymerizing the secondcolor liquid crystal; cutting the assembly to expose a third opening ofthe third LC channel; injecting a third color liquid crystal in thethird LC channel; and polymerizing the third color liquid crystal. 13.The fabrication method for a color cholesteric liquid crystal displaydevice as claimed in claim 12, wherein each of the first color liquidcrystal, the second color liquid crystal, and the third color liquidcrystal comprises a polymer dispersed liquid crystal (PDLC).